In conventional cases, in order to update system software of a mobile communication terminal such as a cellular phone, it is necessary to connect the mobile communication terminal to a PC (Personal Computer), in which software dedicated to download is installed via a special cable and the system software is downloaded to the mobile communication terminal by activating download software that is dedicated to downloading software. However, in such a method, it is necessary for a user to prepare both the PC in which the download software is installed and use the special cable as described above. This is a problem because it is very inconvenient.
In order to solve this problem, Patent Document 1 (Unexamined Japanese Patent Application, First Publication No. 2001-078258) discloses a technique in which system software is automatically downloaded via a network from a system software distribution center connected to a communication network. In accordance with this technique, it is possible to download the system software to the mobile communication terminal without setting up a PC in which the download software is installed and using a special cable as described above. However, while downloading, usage of the mobile communication terminal by the user is prevented (a state of the mobile communication terminal is set so as to be unusable). Moreover, there is another problem in which downloading can be interrupted due to a shortage of power from a battery while downloading. In Patent Document 2 (Japanese Patent Unexamined Application, First Publication No. 2002-111573), in order to solve such the problem of low-battery, a technique is disclosed in which the system software is only downloaded if the mobile communication terminal is in a charged state.
In accordance with the technique disclosed in the above-described Patent Document 2, it is certain that an interruption of downloading due to a low-battery is prevented because the system software is automatically downloaded while the mobile communication terminal is in a charged state. However, there are cases in which the user would like to operate the mobile communication terminal while charging the battery, for example, receive an incoming call or receive email. Therefore, in such cases, even by using the technique disclosed in the above-described patent document 2, the usage of the mobile communication terminal is limited if the download is started. Therefore, even by using the technique disclosed in the above-described patent document 2, the problem of preventing the usage of the mobile communication terminal by the user is not solved.